Manufacture of motor fuel from sludge oil



G. ARMISTEAD, JR., ET AL MANUFACTURE OF MOTOR FUEL FROM SLUDGE OIL Filed July 8, 1951 1 N v E N TO R s @5000: ARM/5154mm WALTER ULL/PICH ATTORNEY June 18, 1935.

Patented June 18,1935

UNITED STATES MANUFACTURFQLOF MOTOR mar. raoM UDGE OIL George Armistead, Jr., Lockport, 111., and Walter Ulll'leh, Port Arthur, Ten,

assignors to The .Texas Company, New York, N. Y., a corporatlon of Delaware Application July 8, 1931, Serial No. 549,568

llOlaims.

This invention relates to the manufacture of cracked motor fuel by the thermal conversion of oil recovered from sludge obtained in the refining of hydrocarbon oils.

The invention contemplates a process for the manufacture of motor fuel of high anti-knock qualities comprising distilling crude petroleum for the production of lubricating oil stock, treating the resulting stock withstrong mineral acid to remove; therefrom, in the form of a sludge, hydrocarbon constituents .unsuitable for lubricating purposes, treating the sludge to separate therefrom hydrocarbon oil whichis subjected to partial distillation to form a stock substantially free from mineral acids and adapted for cracking, and then subjecting. the separated hydrocarbons to cracking under suitable conditions for the production of cracked motor fuel.

Lubricating oil containing fractions, and more 20 particularly heavy or residual fractions of the cylinder stock type, as obtained from crude petroleum, usually contain substantial proportions of unsaturated and tarry-like constituents whose presence is unsuitable in finished lubricating oils and which are, therefore, removed from the lubricating oil fractions in the form of a sludge during subsequent treatment with a strong mineral acid. This sludge, composed largely of polymerized, sulphonated and oxidized hydrocarbons, has been, in the past, after separation therefrom of dilute acid,-disposed of. as fuel or utilizedto some extent in the production of certain types of asphaltic material.

' The prior art has also included treatment of this sludge material by first neutralizing its acidic bodies with lime and then reducing the neutralized sludge to coke by destructive distillation. The distillateresulting from this method;

of treatment is composedsubstantially of hyhigher while the resulting coke on account of its.

lime content is unsatisfactory for fuel purposes.

However, this sludge materiahwhen properly conditioned to free it of undesirable mineral acidic constituents and other corrosive substances as well 'asthe' relatively more coke like components-i's particularly suitablefor cracking for the production--of= high-grade'moto'r fuel possessing acid-treatedoil spe nrii (1-stoset v for high anti-knock qualities. 1 a 0, Our-process; therefore, comprises-"distilling crude oil for the production of a lubricating 'oil fractiongsuch is cylinder s'tock',=;and1 which may comprise either a residual stock, such as obtained,

- by ordinary" distillation at atmospheric pressure,

by distilling crude at subatmospheric pressures. The resulting lubricating oil stock is then subjected to treatmentwith strong mineral acid to remove tarry and unstable hydrocarbon constituents as a sludge which may comprise as much 5 as 30 to 40 per cent or even more of the original lubricating oil stock. This sludge may then bemixed with a substantial proportion of water which latter serves as a medium for washing out the retained and partially spent acid and,,in 10 addition is mixed with agrelatively large quantityof gas oil or-other hydrocarbon oil, suitable as a diluent, for cutting back and increasing the fluidity of the sludge undergoing treatment.

' This resulting-mixture. is then subjected. to 15 cooking and steaming to resolve the sludge into a substantiallyfluid condition and facilitate sepa-' ration therefrom of liquid hydrocarbons, accompanied also. by a'separauon ofaqueous and acidic material, during subsequent settling. The separated liquid hydrocarbons obtained ,during the settling step may then be subjected to cracking advantageously undersuper-atmospheric pressures rangi as highas 400 pounds'or more, at temperatures which may range from 750 to 950 F. or higherand then fractionating the resulting cracked products to recover the cracked gasoline constituents. p

By way of illustrating in greater detailthe process of carrying out our, invention, crude petroleum, for example, of the type obtained in the mid-continent fields, is distilled, preferably at substantially atmospheric DIGSSUIGMEO remove its low boiling constituents which may include gasoline, kerosene, gas oil and wax distillate, and form a residual cylinder stock fraction which latter may comprise from 25% to 30% of .the original crude and have a viscosity of from 100 to 130 Saybolt-Universalseconds at 210 F. E

This cylinder stock fraction is introduced to an 40 agitator wherein it-may beagitated with from about 35 to 50 pounds per barrelof 98 Be. sulphuric acid, the amount of the acid required dependingupon the desired characteristics of'the final "lubricating" oil product. ment may extend over a periodof minutes while maintaining the mixture at arztemperature; of ,aroundallO F. for example. ;-,Fol lo;win this,

several hours :to \,eilect,cQml- 1Qt Sfiliaration of the particlesof sludge from the treated o After removalsof the acidetreated oil, .t mainingsludgej-is mixed with-wateranda iluent; gas Broil, in approximately the 5 proportion; parts of sludge with 1 p rt:.otwatemnd 2- The acid, treat-,-: 45

of gas oil. The mixture of sludge, oil and water is then subjected to cooking by the introduction of open steam, the cooking operation being carried out at a temperature of around 220 F. and extending over a period which may range from 8 to 24 hours, after which the mixture is allowed to settle and form two layers. The upper layer comprises liquid hydrocarbons separated from the sludge in admixture with the diluent gas oil and containing small amounts of acid. The bottom layer is composed of a mixture of heavy cokelike sludge particles, water and spent acid.

After removal of the upper layer, the remaining bottom layer, after drawing off the separated aqueous portion, is advantageously subjected to further dilution, including, if desired, neutralization with alkaline material and then cooking in substantially the same manner as in the preceding step for the purpose of separating additional liquid hydrocarbons from the sludge and which hydrocarbons are added to the hydrocarbon mixture at first separated. Repetition of this dilution and cooking treatment may be carried out to whatever extent necessary in order to effect the desired degree of liquid hydrocarbon recovery. The total recovered liquid hydrocarbons may comprisefrom around 60% to 70%, or even more, by volume of the original sludge.

The heavy sludge or vcoky material remaining from the cooking operation is not particularly desirablefor commercial cracking since it is not only of a very coky nature and therefore productive of a large amount of coke but it also retains a considerable amount of acid and acid compounds which, if not removed, would be injurious to the distilling and cracking equipment. When subjected to cracking temperatures, decomposition of these compounds or salts may occur with the liberation of acidic matter, such as sulphur dioxide, for example.

The mixture of recovered liquid hydrocarbons and diluent gas oil usually retains small amounts of acidic material, which, unless removed or further suitably treated, would exert an injurious efiect upon the cracking apparatus. Therefore, we remove these acidic or corrosive constituents by first subjecting the hydrocarbon mixture to a preliminary distillation wherein the aqueous material is volatilized and any salt compounds, decomposable on heating, may also be broken down to liberate acidic matter, all of which is removed along with a small amount of relatively low boiling hydrocarbon constituents, serving as a stripping medium. This distillate is advantageously removed and condensed in the presence of an alkaline material, such as lim,-'soda ash or caustic, and the like, to neutralize its corrosive effect and thus protect the still equipment. The amount of hydrocarbon constituents removed in this operation may be varied at will.

Thus, if desired, substantially all of the diluent oil may be removed in this operation and returned.

to recycle through the system as further diluent for fresh sludge. It is advantageous, however,

to leave the bulk of this diluent oil, which is itself suitable for cracking, in admixture with the recovered oils, removing just sufficient to effect complete stripping out of the acidic matecracked gasoline product.

rial. This latter operation is of particular advantage 'where the diluent gas oil cmprises a recycle gas oil consisting of the cracked hydrocarbons resulting during the subsequent cracking operation and which are ofrelatively higher boiling point than that desired for the desired The resulting partially distilled hydrocarbon oil mixture, substantially free from acidic material, is then subjected to cracking advantageously in cracking apparatus of the coil and drum type wherein it is heated to a temperature of around 900 F. and under a pressure of from 100 to 250 pounds. The particular operating temperatures and pressures employed may be varied, depending upon the nature of the particular stock, or upon the degree to which it has been reduced in the preliminary distilling operation. Thus, if only a small portion of the diluent and relatively more refractory gas oil and lighter hydrocarbon constituents have been removed in this preliminary distillation operation, the subsequent cracking operation may be carried out at relatively high temperatures and pressures, whereas if the stock has been reduced so as to remove substantially all of the diluent gas oil added. thereto during the initial treatment of the sludge, then the cracking temperatures and pressures may advantageously be modified to somewhat lower values.

The stock, particularly where the greater portion of the diluent gas oil has been removed, and comprises hydrocarbons from which carbon may be readily deposited on the interior surfaces of heating coils, may be suitably cracked in coil and drum cracking apparatus wherein the fresh charge is brought into contact with a generated stream of cracked vapors, thereby vaporizing its gas oil constituents which, together 'with partially converted and more refractory fractions, form a clean stock comparatively free from constituents rich in carbon and; therefore, adapted for circulation through the cracking coil at relatively high temperatures without substantial coke formation.

The resulting cracked products are fractionated, preferably while under pressure derived from the cracking reaction, to separate the desired cracked gasoline components, while the heavier fractions are returned to the coil for further heating. The pressure tar formed during this operation is subjected to a stripping action'in the manner customarily employed in regular cracking operations to remove, besides gasoline constituents, the heavier and intermediate constituents or recycle gas oil. All or a portion of this recycle gas oil may be used as a diluent or solvent in the initial treatment of the acid sludge to prepare fresh cracking stock therefrom. That portion not used in treating the sludge may be returned directly to the cracking, apparatus.

When cracking under substantially the foregoing conditions, a stock of around 14 B. gravity and having a viscosity of 700 seconds at 122 Saybolt Furol, a cracked gasoline fraction of around 410 end point may be obtained having an anti-knock value of 68 expressed in terms of octaine numbers.

While cracking may be effected at superatmospheric pressures, as above described, it is contemplated that the recovered hydrocarbons, either with or without having first removed the diluent gas oil, may be subjected to destructive distillation in a shell type of still maintained under substantially atmospheric pressure to produce a cracked fraction and coke. This cracked fraction may then be fractionated to remove its gasoline constituents and form a gas oil fraction which is suitable for further cracking under pressure.

In the drawing the single figure represents diagrammatically an oil treating system embodying form two layers.

my invention. Referring more particularly to the drawing reference numeral I indicates a crude still into which oil to be treated may be charged through pipe 2. Three (3) indicates a fire box for supplying the necessary heat. In the still the oil is heated to such a temperature that the lighter fractions thereof pass off as vapors through line 4 into any suitable fractionating equipment 5, the amount of oil so vaporized being sumcient to leave in the still I a lubricating oil fraction, which may be for example, of the cylinder stock range of viscosity. Where the fresh oil charge to the still is a crude petroleum, for example, of the type obtained in the mid-continent fields, the residual stock remaining in the still I after removal of the lighter fractions may comprise from 25 to 30% of the original charge and have a viscosity of from 100 to 130 Saybolt Universal seconds, at 210 F., the lighter fractions distilled oflLincluding gasoline, kerosene, gas oil and wax distillate. The residual oil is drawn off through line Shavin therein a cooler 'l and is introduced by pump 8 into the top of an agitator 9. In this agitator reaction of the oil with strong mineral. acid, introduced through line It, takes place. This acid may be, for example, 98 Baum sulphuric acid, the amount of acid used being, for example, from 35 to 50 pounds per barrel of oil. After acid treatment for a period of, for example, 45 minutes, at a temperature of around 110 F. the acid treated oil is permitted to settle for several hours, to effect complete separation of the particles of sludge from the treated oil. The acid treated oil comprising the top-layer, indicated by reference numeral H, may be drawn off through a line l2 while the heavy sludge is transferred through line I; into tank l4.

Water and diluent gas oil are introduced into the tank l4 through lines l5 and I6 nespectively, the oil serving to dilute the sludgeand the water to wash the acid therefrom. The mixture of sludge oil and water is then subjected to cooking by the introduction of open steam through line I H, the cooking operation being carried out'at a temperature of around 220 F. and extending over a period which may range from 8 to 24hours, after which the mixture is allowed to settle and The upper layer 18 comprises liquid hydrocarbons separated from the sludge in admixture with diluent gas oil and contains small amounts of acid. The bottom layer is is composed of a mixture of heavy coke-like sludge particles, water and spent acid. Twenty (20) indicates a separated aqueous portion consisting of water and the acid washed out thereby. The aqueous portion, and the heavy sludge or coky material remaining from the coking operation,

' maybe withdrawn from the tank. l4 through drawofl line 2i, while the mixture of recovered liquid hydrocarbons and diluent gas oil, which usually retains small amounts of acidic material,

is drawn of! through the line 22 and is subjected to distillation, for example in the shell still 23,

heated by a furnace. .In this still the tem'-,

26 wherein they may be condensed and neutralized by the addition of lime, soda ash, caustic or the like through line 28, the condensate being collected in receiving drum 21. When operating in this manner valve 66 is closed and valve 65 open. Any desired portion of the resulting condensate may be returned to the tank through line 29, by'action of pump 30, any remainder being diverted from the process through pipe 3|. After the preliminary distillation of acidic material from the liquid hydrocarbons in the still 23 the remaining, substantially acid free, oil may be removed through line 32 having valve 32 and pump 33 for introduction into a first fractionating column 34 of a cracking system indicated generally by reference numeral 35. Condensate is removed from the bottom of the fractionator 34 and returned through pipe36 having pump 3'I-into still 28, while light vapors pass overhead from the fractionator 34 entering the second fractionator 30 wherein they undergo a further partial condensation. Light vapors of products suitable for use as motor fuel pass overhead through line 40 then through condenser 4| into receiving drum 42, while reflux condensate-collecting in the bottom of the fractionator 39 and constituting a clean cracking condensate, is withdrawn through conduit 43 and forced by pump 44 through cracking heater or furnace 45, wherein it is heated to an effective cracking temperature, which may be for example around 900 F., the pressure on the products passing from the heater being, for example, for 100 to 250 pounds per square inch. The highly heated products are then passed through the pipe 46 into the still 38, wherein a. cracking temperature is maintained and further cracking occurs.

Liquid residue produced in still 38 may be drawn off from time to time or continuously through drawoff line 41, and passed through reducing valve 48 into'flash drum 49. In the flash drum the acid sludge to prepare fresh cracking stock therefrom, in the manner explained hereinbefore. The remaining portion not so used may be returned through conduit 56, to the cracking process. Heavy liquid residue may be drawn off from the flash drum 49 through pipe 51.

Instead of being transferred to the cracking unit 35, the recovered hydrocarbons withdrawn from tank l4 may be subjected to destructive distillation in the still 23, either with or without prior removal of the diluent gas oil, under substantially atmospheric pressure to produce a cracked fraction and coke. This cracked fraction may then be fractionated in fractionator to remove its gasoline constituents which pass off through vapor line BI and condenser 62 into receiver 63, and form a gas oil fraction'which is suitable for further cracking under pressure. This gas oil fraction may be withdrawn through line 64, as

reflux condensate, and introduced into line 32 for cracking in the cracking system 35. In this case valve 65 would be closed and valve 66 open.

Obviously, for continuous operation, several agitators 9 and settling tanks l4 may be provided so that while some of them are being permitted to settle, others may be used for mixing fresh charges.

If desired the wax distillate or other lubricating oil fraction from fractionator 5 may be treated as described hereinbefore, this fraction being transferred to line 6 through conduit 61. Oil may be diverted from the process through valved pipes 68 and 69 whenever desired.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A method of producing cracked motor fuel of high anti-knock properties which comprises distilling crude petroleum and forming therefrom a lubricating oil fraction of the cylinder stock range of viscosity, subjecting the fraction to treatment with strong mineral acid and thereby producing a heavy sludge containing polymerized,

sulphonated and oxidized hydrocarbons, mixing approximately three parts of the sludge with approximately one part of water and two parts of gas oil, subjecting the mixture to cooking in the presence of open steam to facilitate separation of liquid hydrocarbons and aqueous material from the sludge, permitting the cooked mixture to settle and separating therefrom liquid hydrocarbons suitable for cracking and comprising around 60% of the original sludge, subjecting the separated hydrocarbons and diluent oil to preliminary distillation to remove retained acidic material and a substantial portion of the diluent gas oil, which is returned for treating further sludge, subjecting the remaining oil composed substantially of recovered sludge oil to continued and destructive distillation at relatively higher temperature and then fractionating the resulting cracked product to produce motor fuel.

2. A method of producing cracked motor fuel of high anti-knock properties which comprises distilling crude petroleum and forming therefrom a lubricating oil fraction of the cylinder stock range of viscosity, subjecting the fraction to treatment with strong mineral acid and thereby producing -a heavy sludge containing polymerized,

sulphonated and oxidized hydrocarbons, mixing approximately three parts of the sludge with approximately one part of water and two parts of gas oil, subjecting the mixture to cooking in the presence of open steam to facilitate separation of liquid hydrocarbons and aqueous material from the sludge, permitting the cooked mixture to settle and separating therefrom an upper layer of liquid hydrocarbons suita ble for cracking, subjecting the separated hydrocarbons'and diluent oil to preliminary distillation to remove retained acidic material and produce a substantially mineral acid-free cracking stock, subjecting said stock, while still retaining heat from said distillation, to cracking under superatmospheric pressure and at temperatures of over 750 F. and then fractionating the cracked products to produce motor fuel.

3. A method of producing cracked motor fuel of high anti-knock properties which comprises distilling crude petroleum and forming therefrom a lubricating oil fraction of the cylinder stock range of viscosity, subjecting the fraction to treatment with strong mineral acid and thereby producing a heavy sludge containing polymerized, sulphonated and oxidized hydrocarbons, steaming the sludge in the presence of water and diluent gas oil to facilitate separation of liquid hydrocarbons and acidic material from the sludge, permitting the cooked mixture to settle and separating therefrom an upper layer of liquid hydrocarbons suitable for cracking, subjecting the separated hydrocarbons and diluent oil to distillation to remove retained acidic material and produce a substantially mineral acid-free cracking stock, subjecting said stock, while still retaining heat from said distillation, to cracking under superatmospheric pressure and at temperatures of over 750 F. and then fractionating the cracked products to produce motor fuel.

4. A method of producing cracked motor fuel of high anti-knock properties which comprises distilling crude petroleum and forming therefrom a lubricating oil fraction of the cylinder stock range of viscosity, subjecting the fraction to treatment with strong mineral acid and thereby producing a heavy sludge containing polymerized, sulphonated and oxidized hydrocarbons, diluting said sludge with recycle gas oil formed during subsequent cracking, adding water and subjecting the mixture to cooking in the presence of open steam to facilitate separation of liquid hydrocarbons and aqueous material from the sludge, permitting the cooked mixture to settle and separating therefrom an upper layer of liquid hydrocarbons suitable for cracking, subjecting the separated hydrocarbons and diluent oil to distillation to remove retained acidic material and produce a substantially mineral acid-free cracking stock, subjecting said stock, while still retaining heat from said. distillation, to cracking under superatmospheric pressure and at temperatures of over 750 F., fractionating the cracked products to produce motor fuel, and returning a portion of the relatively high boiling cracked products as a recycle gas oil for diluting further sludge.

5. A method of producing cracked motor fuel of high anti-knock properties which comprises distilling crude petroleum'and forming therefrom a lubricating oil fraction of the cylinder stock range of viscosity, subjecting the fraction to treatment with 98% sulphuric acid and thereby producing a heavy sludge containing polymerized, sulphonated and oxidized hydrocarbons, mixing approximately three parts of the sludge with approximately one part of water and two parts of gas oil, subjecting the mixture to cooking in the presence of open steam, permitting the mixture to settle and form an upper layer comprising recovered liquid hydrocarbons and diluent gas oil, and a bottom layer composed largely of heavier coke-like hydrocarbons, water and dilute mineral acid, removing the upper layer, subjecting the bottom layer after removal of the separated aqueous material to further dilution and cooking to recover additional liquid hydrocarbons which are mixed with the hydrocarbons first removed, subjecting the mixture of recovered hydrocarbons and diluent gas oil to distillation to remove retained acidic material and produce substantially mineral acid-free cracking oil stock, while still retaining heat from said distillation, subjecting said stock to cracking under pressures of the order of 100pounds per square inch or higher and at a temperature of over 750 F. and then fractionating the cracked product to produce motor fuel.

6. The method of producing cracked motor fuel of high anti-knock properties which comprises distilling crude petroleum and forming therefrom a lubricating oil fraction of the cylinder stock range of viscosity, subjecting the fraction to treatment with strong mineral acid and thereby producing a heavy sludge containing polymerized, sulphonated and oxidized hydrocarbons, mixing approximately three parts of the sludge with approximately one part-of water and two parts of gas oil, subjecting the mixture to cooking in the presence of open steam to facilitate separation of liquid hydrocarbons and aqueous material from the sludge, permitting the cooked mixture to settle and separating therefrom liquid hydrocarbons suitable for cracking and comprising around 60% of the original sludge, subjecting the separated hydrocarbons and diluent oil to preliminary distillation to remove retained acidic material and a substantial portion of the diluent gas oil, which is returned for treating further sludge, subjecting the remaining oil composed substantially of recovered sludge oil to continued and destructive distillation at relatively higher temperature to produce coke and vapors, fractionating said vapors to separate therefrom gasoline constituents and a gas oil fraction and cracking said gas oil fraction under pressure.

7. The method of producing cracked motor fuel from acid sludge produced by the treatment of a hydrocarbon lubricating oil fraction with a strong mineral acid, which comprises mixing said sludge with a diluent oil to reduce the viscosity thereof so that it may be settled into layers, mixing water with the diluted sludge and cooking the mixture by direct contact with steam to facilitate separation of liquid hydrocarbons and aqueous material from the sludge, permitting the cooked mixture to settle and separate into an upper layer of liquid hydrocarbons, and a lower layer of heavy sludge or coky material having an aqueous portion, removing liquid hydrocarbons from said layer first mentioned, subjecting the removed liquid hydrocarbons to preliminary heating to distill therefrom retained acidic material and a portion' of said diluent oil, subjecting remaining oil to cracking conditions of temperature and pressure to cause cracking thereof, and fractionating the resulting cracked vapors to produce motor fuel.

8. A method according to claim '7 wherein a relatively light oil derived from said liquid hydrocarbons is utilized as diluent for additional acid sludge.

9. The method of producing cracked motor fuel from acid sludge produced by the treatment of a hydrocarbon lubricating oil fraction with a strong mineral acid, which comprises mixing said sludge with a diluent oil to reduce the viscosity thereof so that it may be settled into layers, mixing water with the diluted sludge and cooking the mixture by direct contact with steam to facilitate separation of liquid hydrocarbons and aqueous material from the sludge, permitting the cooked mixture to settle and separate into an upper layer of liquid hydrocarbons, and a lower layer of heavy sludge' or coky material having an aqueous portion, removing liquid hydrocarbons from said layer first mentioned, subjecting the removed liquid hydrocarbons to preliminary heating to distill therefrom retained acidic material and a portion of said diluent oil, subjecting remaining oil to destructive distillation to produce a cracked fraction and coke, and fractionating said cracked fraction to separate gasoline constituents therefrom.

10. A method of producing cracked motor fuel of high anti-knock properties which comprises distilling crude petroleum and forming therefrom a lubricating oil fraction of the cylinder stock range of viscosity, subjecting the fraction to treatment with strong mineral acid and thereby-producing a heavy sludge containing polymerized, sulphonated and oxidized hydrocarbons, mixing with the sludge a substantial proportion of water and a relatively large quantity of diluent gas oil, subjecting the mixture to cooking in the presence of open steam to facilitate separation of liquid hydrocarbons and aqueous material from the sludge, permitting the cooked mixture to settle and separating therefrom liquid hydrocarbons suitable for cracking and comprising around 60% of the original sludge, subjecting the separated hydrocarbons and diluent oilto preliminary distillation to remove retained acidic material and a substantial portion of the diluent gas oil, which is returned for treating further sludge, subjecting the remaining oil composed substantially of recovered sludge oil to continued and destructive distillation at relatively higher temperature and then fractionating the resulting cracked product to produce motor fuel.

11. A method of producing cracked motor fuel of high anti-knock properties which comprises distilling crude petroleum and forming there-' from a lubricating oil fraction of the cylinder stock range of viscosity, subjecting the fraction to treatment with strong mineral acid and thereby producing a heavy sludge containing polymerized, sulphonated and oxidized hydrocarbons, mixing with the sludge a substantial proportion of water and a relatively large quantity of diluent gas oil, subjecting the mixture to cooking in the presence of open steam to facilitate separation of liquid hydrocarbons and aqueous material from the sludge, permitting the cooked mixture to settle and separating therefrom an upper layer of liquid hydrocarbons suitable for cracking, subjecting the separated hydrocarbons and diluent oil to preliminary distillation to remove retained acidic material and produce a substantially mineral acid-free cracking stock, subjecting said, stock, while still retaining heat from said distillation, to cracking under superatmospheric pressure and at temperatures of over 750 F. and then fractionating the cracked products to produce motor fuel.

GEORGE ARMISTEAD, JR. WALTER UILRICH. 

